Fatal error: Cannot access empty property

Hello,

First, thanks for this useful module !
I just updated to content level 1.1-rc1 and I have this fatal error when not logged in with user 1 (admin) on some pages : frontpage, some views with custom templates using a content level field, add/edit node forms. /user page is fine and other views pages not using the content level field are fine too.

Fatal error: Cannot access empty property in […]/sites/all/modules/content_levels/content_levels.module on line 372

I ran update.php and cleared the cache. I have no idea what is happening there.

Content Construction Kit (CCK) 6.x-2.8
Views 6.x-2.11
Drupal core 6.19
And other modules I can list if needed ;)